A communication system is a facility that enables communication between two or more entities such as user terminal equipment and/or network entities and other nodes associated with a communication system. The communication may comprise, for example, communication of voice, electronic mail (e-mail), text messages, data, multimedia and so on.
The communication may be provided by a fixed line and/or a wireless communication interface. A feature of wireless communication systems is that they provide mobility for the users thereof. An example of communication systems providing wireless communication are public land mobile networks (PLMN). An example of the fixed line system is a public switched telephone network (PSTN).
A communication system typically operates in accordance with a given standard or specification which sets out what the various elements of a system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched server or a packet switched server or both. Communication protocols and/or parameters which should be used for the connection are also typically defined. For example, the manner in which the communication should be implemented between the user equipment and the elements of the communication networks is typically based on a predefined communication protocol. In other words, a specific set of “rules” on which the communication can be based needs to be defined to enable the user equipment to communicate via the communication system.
So called third generation communication systems are being introduced. These so called third generation systems use code division multiple access techniques. One example of such a third generation communication system is the cdma2000 system.
When a mobile node (MN) moves and changes its point of attachment to the Internet, there is a period of time when it is not able to send packets because of the link switching delay and IP configuration procedures. Reference is made to the document “Fast Handovers for Mobile IP (Internet Protocol)v6—A Draft IETF (Internet Engineering Task Force) Specification (draft-ietf-mipshop-fast-mipv6-01.txt)”. As discussed in this document, fast handoffs for IPv6 enable a mobile node to minimise this handoff latency by moving operations such as router discovery, IP address configuration and signalling the correspondent nodes to update its location out of the critical period when the mobile node is handing off. The proposed procedure discussed in this document for the fast handoff protocol involves setting up temporary forwarding for the traffic meant for the mobile node from the previous router to the new access router. To set up this forwarding, the mobile node needs to know the IPv6 global address of the previous access router so that it can send a fast binding update message to the previous access router.
In cdma2000 networks, when the mobile node requests a simple IPv6 service, it configures a topologically correct IPv6 address from the IPv6 prefix advertised by the PDSN (Packet Data Serving Node). If the mobile node moves and attaches to a different PDSN there is a period of time when the mobile node is not able to receive packets. The IPv6 address is configured during the IPv6CP:IPv6 Control Protocol phase of the PPP (Point-to-Point Protocol) set up between the mobile node the PDSN. However, in the CDMA 2000 networks, the PDSN only configures a link local address on the PPP link and does not configure a global address from the prefix advertised on the PPP link. The mobile node only knows the link local address of the PDSN. A link local address is one which is valid only on a link. In other words, a different link can have a different link address. A unicast global address has a global routing prefix which is a (typically hierarchically-structured) value assigned to a site (a cluster of subnets/links), a subnet ID identifying a link within the site and an interface ID. This is discussed in IETF document RFC 3513. Thus a link local address is valid only on a link whereas a global unicast address is globally routable.
Even if the PDSN were to configure a global address from the prefix advertised on the PPP link and inform the mobile node of the global address, it would still not be possible for the mobile node to send a fast binding update to the old PDSN from the new PDSN, if the mobile node hands off to a new PDSN. This is because the PPP link between the mobile node and the old PDSN is terminated when the mobile node moves to a new link and the PDSN's global address is no longer valid.
It is an aim of embodiments of the present invention to address or at least mitigate the above described problem.